When areas of a glass ceramic plate are exposed to large temperature changes during operation, for a wide variety of reasons it is necessary to know the temperatures in these areas. Typically, in the case of cooking areas with glass ceramic plates as cooking surfaces, the temperature in the cooking zone must be monitored continuously during operation. When the temperature/time load capacity of the glass ceramic plate is exceeded, the latter may break. The temperature must also be detected to regulate the output of the cooking zone.
The temperature of the glass ceramic plate in the cooking zone is usually monitored with the aid of a rod expansion regulator. Such an arrangement has been disclosed by, for example, EP 0 394 693. The corresponding expansion-rod temperature sensor is mounted several millimeters from the lower side of the glass/glass ceramic plate and thus does not directly detect the temperature that prevails at the measuring site (cooking zone).
Consequently, it reacts only with a time lag and, in many cases, responds incorrectly to changes in temperature.
There are also proposals to use the infrared radiation of the lower side of the hot glass ceramic plate to determine temperature. In the sample application, the conversion did not work because the coil of the heating unit that heats up the cooking zone radiates at the same wavelength and distorts the information signal.